1. Field of the Invention
The present invention relates to an apparatus for sticking a sheet material for use in sticking a sheet material with an adhesive on one side thereof to a work such as picture tube for television having a flat screen.
2. Prior Art
In manufacturing process of a picture tube for television, at the last stage thereof, a coating film is formed on the surface of the picture tube screen in order to increase picture quality and prevent diffused reflection. This coating film is formed by the steps of supporting the picture tube with its screen upward, turning it on a vertical axis, and spreading a coating film liquid supplied on the center of the screen uniformly toward the periphery of the screen with centrifugal force. It is, however, a recent trend that picture tubes for television have flat screens, which makes it difficult to form a uniform film on the screen by the conventional method for forming a coating film. The difficulty especially increases as the screen size increases.
In order to cope with the increasing trend toward the flat screen of picture tubes, instead of forming a coating film on the screen surface, a method in which a sheet material which functions like a coating film is stuck onto the screen surface has been recently employed. And for carrying out this method, an apparatus for sticking a sheet material has been developed. As shown in FIG. 6, this known apparatus for sticking a sheet material comprises: a picture tube supporting and conveying mechanism (not shown) for supporting a picture tube 1 with its screen upward and conveying the picture tube 1 in horizontal direction; a sheet material transferring member 3 for holding a sheet material 2 and transferring the sheet material 2 to the screen of the picture tube 1; and a pressure roller 4 for pressing a part of the sheet material 2 on the screen of the picture tube 1.
The sheet material transferring member 3 consists of a flat box member 5a of which plan view is a rectangular shape of a size substantially equal to that of the sheet material 2. One face of the box member 5a is of a porous sucking plate 6a having a large number of through holes. The box member 5a is provided with a sucking mouth 7a, and the sucking mouth 7a is connected to an intake blower (not shown) so that the air inside of the box member 5a may be sucked up. An adhesive is applied on one face of the sheet material 2. A sucking force acts on the sheet material 2 through the large number of through holes of the porous sucking plate 6a, whereby the porous sucking plate 6a of the sheet material transferring member 3 sucks the other face of the sheet material 2 where an adhesive is not applied. The sheet material 2 is held by the sheet material transferring member 3 with a part of the sheet material 2 slightly protruding from the porous sucking plate 6a. The sheet material transferring member 3 is supported by a transferring member supporting and moving mechanism not shown in the drawing, and reciprocates between a sheet material sticking position shown in FIG. 6 where the sheet material 2 sucked and held on the porous sucking plate 6a faces the screen of the picture tube 1 and a sheet material delivery position not shown in the drawing where sheet materials 2 are delivered one by one to the porous sucking plate 6a. The sheet material transferring member 3 is supported so that its forward side in the conveying direction of the picture tube 1 may be slightly inclined downward (descend) at the sheet material sticking position.
The pressure roller 4 is located on the forward side from the sheet material transferring member 3 in the conveying direction of the picture tube 1 at the sheet material sticking position so that the pressure roller 4 may come near the sheet material transferring member 3 and cross the conveying direction of the picture tube 1 at a right angle. The pressure roller 4 is rotatably supported and driven to move slightly in vertical direction. When the sheet material 2 is stuck on the screen of the picture tube 1, the pressure roller 4 moves downward and presses a part of the sheet material 2 on the screen of the picture tube 1.
In the foregoing known apparatus for sticking a sheet material, the sheet material is stuck to the picture tube as described below.
First, at the sheet material delivery position, sheet materials are supplied one by one from a sheet material supplying mechanism not shown to the sheet material transferring member 3, and one sheet material 2 is sucked and held on the porous sucking plate 6a of the sheet material transferring member 3. Then, the sheet material transferring member 3 moves to the sheet material sticking position, and the picture tube 1 is delivered to the sheet material sticking position. Then, with the sheet material 2, which is sucked and held on the porous sucking plate 6a of the sheet material transferring member 3, facing the screen of the picture tube 1, the pressure roller 4 moves downward to press a front edge portion of the sheet material 2 protruding from the porous sucking plate 6a on the screen of the picture tube 1, whereby the portion is stuck on the screen of the picture tube 1 with an adhesive. With the pressure roller 4 pressing a part of the sheet material 2 on the screen of the picture tube 1, the picture tube 1 is moved forward, whereby a friction force is generated and the generated friction force rotates the pressure roller 4. Thus, the sheet material 2 is gradually stripped from the porous sucking plate 6a of the sheet material transferring member 3 and is gradually stuck on the screen of the picture tube 1. Finally, the whole sheet material 2 is stripped from the porous sucking plate 6a of the sheet material transferring member 3, and the whole sheet material 2 is stuck on the whole screen of the picture tube 1.
After the sheet material 2 is completely stuck to the picture tube 1, the sheet material transferring member 3 moves to the sheet material delivery position and receives a sheet material from the sheet material supplying mechanism. The foregoing operation is repeated, and the sheet material 2 is stuck on a next coming picture tube 1.
FIG. 7 illustrates an example of another construction of a sheet material transferring member in a conventional apparatus for sticking a sheet material. In the same manner as the foregoing sheet material transferring member, this sheet material transferring member 8 comprises a flat box member 5b which is shaped into a rectangle in a plan view with one face consisting of a porous sucking plate 6b having a large number through holes. The box member 5b is provided with a sucking mouth 7b connected to an intake blower. In this sheet material transferring member 8, a number of small rollers 9 are rotatably mounted on the whole face of the porous sucking plate 6b. In this sheet material transferring member 8, the sheet material 2 is sucked and held on the porous sucking plate 6b with the sheet material 2 in contact with the number of small rollers 9. The sheet material 2 is stripped from the porous sucking plate 6b with the number of small rollers 9 making a rolling contact with the sheet material 2 when the sheet material 2 is stuck on the screen of the picture tube 1.
In the apparatus for sticking a sheet material constructed as shown in FIG. 6, when the sheet material 2 is stuck on the screen of the picture tube 1, the sheet material 2 is stripped from the porous sucking plate 6a of the sheet material transferring member 3 while being in rolling contact with the porous sucking plate 6a. There is a possibility that this causes linear scratches on the surface of the sheet material 2. The scratches on the surface of the sheet material 2 stuck on the screen of the picture tube 1 give a negative influence on the performance of the picture tube 1. Even when the porous sucking plate 6a is made of a material of extremely small in coefficient of friction in order to prevent such scratches, it is impossible to completely prevent occurrence of the scratches. In addition, when foreign matter such as dust is on the surface of the porous sucking plate 6a, it is probable that more scratches are formed on the surface of the sheet material 2.
In the sheet material transferring member 8 shown in FIG. 7, when the sheet material 2 is stuck on the screen of the picture tube 1, the sheet material 2 makes a rolling contact with the number of small rollers 9. Therefore, it is certain that less scratches are formed on the surface of the sheet material 2 as compared with the sheet material transferring member 3 shown in FIG. 6. But, it is impossible to completely prevent scratches on the sheet material 2 even in this sheet material transferring member 8. When foreign matter such as dust sticks onto the small rollers 9 to the extent that some of rollers 9 do not rotate smoothly, linear scratches come to be formed on the surface of the sheet material 2 in the same manner as those in the sheet material transferring member 3 shown in FIG. 6.